From 90389ec3c2d84064979c43f56d3b3b3c09e5e08c Mon Sep 17 00:00:00 2001
From: Khalim Conn-Kowlessar <kconnkowlessar@gmail.com>
Date: Mon, 2 Feb 2026 15:54:22 +0000
Subject: [PATCH] added loft_insulated_at_rafters_efficiency

---
 backend/onboarders/epc_descriptions.py | 37 +++++++++++++++++++++++---
 1 file changed, 33 insertions(+), 4 deletions(-)

diff --git a/backend/onboarders/epc_descriptions.py b/backend/onboarders/epc_descriptions.py
index fc10ad70..d2237880 100644
--- a/backend/onboarders/epc_descriptions.py
+++ b/backend/onboarders/epc_descriptions.py
@@ -598,11 +598,40 @@ def loft_insulated_at_rafters_efficiency_thickness(insulation_thickness: int | N
 def loft_insulated_at_rafters_efficiency_age_band(age_band: EpcConstructionAgeBand) -> EpcEfficiency:
     """
     # 2023 onwards -> Very Good
-    # 2012-2022 -> Good
-    Before 1900 -> Very Poor
-    :param age_band:
-    :return:
+    # 2003-2006, 2012-2022 -> Good
+    # 1983 - 1990, 1996-2002 -> Average
+    # 1976-1982 -> Poor
+    # 1967-1975 and earlier bands -> Very Poor
+    :param age_band: EpcConstructionAgeBand
+    :return: EpcEfficiency
     """
+    year = age_band.start_year()
+    if year >= 2023:
+        return EpcEfficiency.VERY_GOOD
+    if year >= 2003:
+        return EpcEfficiency.GOOD
+    if year >= 1983:
+        return EpcEfficiency.AVERAGE
+    if year >= 1976:
+        return EpcEfficiency.POOR
+
+    return EpcEfficiency.VERY_POOR
+
+
+def loft_insulated_at_rafters_efficiency(
+    insulation_thickness: int | None,
+    age_band: EpcConstructionAgeBand,
+) -> EpcEfficiency:
+    """
+    Combines both age band and insulation thickness to determine loft insulated at rafters roof efficiency.
+    :param insulation_thickness: Insulation thickness in mm
+    :param age_band: EpcConstructionAgeBand
+    :return: EpcEfficiency
+    """
+    if insulation_thickness is not None:
+        return loft_insulated_at_rafters_efficiency_thickness(insulation_thickness)
+
+    return loft_insulated_at_rafters_efficiency_age_band(age_band)
 
 
 ROOF_DESCRIPTION_EFFICIENCIES: Mapping[EpcRoofDescriptions, RoofEfficiencyRule] = {